A long-term evolution/long-term evolution advanced (LTE/LTE-A) system uses a multiple input multiple output (MIMO) technology and a precoding technology, etc., to increase the capacity of the system.
At the receiving side, the user equipment (UE) determines the information that is needed to be fed back, including a Rank Index (RI) and a Precoding Matrix Index (PMI), also referred to as a Codebook Index, and feeds the information back to a base station. At the transmission side, the base station adjusts the precoding matrix to be used based on the information fed back by the UE.
The procedure of determining the RI and the PMI by the receiving side is as follows:
calculating all the metric values (such as equivalent signal to interference-plus-noise ratio (SINR) or capacity, etc.) to which all the precoding matrixes at pilot subcarriers correspond, and then choosing the RI and PMI to which the maximum value in the metric values corresponds (one precoding matrix corresponds to an RI and a PMI) as the information to be fed back to the transmission side. The procedure of determining feedback information by a receiving side in prior art is described below with reference to a drawing.
FIG. 1 is a schematic diagram of selecting feedback information by a receiving side. The description is given taking that a metric value is a SINR as an example. As shown in FIG. 1, following steps are included:
step 101: calculating effective channel matrixes to which all the RIs and PMIs correspond;
wherein a received signal may be expressed as:Y=HWn(l)X+N  (1)
where, Y denotes a vector of the received signal, X denotes a vector of a transmitted signal, and N denotes an additive noise;
an effective channel matrix is: Hn(l)=HWn(l)  (2)
where, H denotes a channel transmission matrix of NR×NT, and Wn(l) denotes a precoding matrix with a rank of l and a codebook index of n;
step 102: calculating metric values to which all the RIs and PMIs in each layer correspond;
wherein the metric values are SINRs, and a minimum mean square error (MMSE) algorithm may be used in calculation; and following formula may be used:
                              SINR                      n            ,            i                                (            l            )                          =                                            [                              Q                n                                  (                  l                  )                                            ]                                      (                              i                ,                i                            )                                            1            -                                          [                                  Q                  n                                      (                    l                    )                                                  ]                                            (                                  i                  ,                  i                                )                                                                        (        3        )            
where, Qn(l)=[( Hn(l))H  Hn(l)+σn2·Il]−1( Hn(l))H  Hn(l), [·](i,i) denotes the ith element in ith row of the matrix, i denotes serial numbers (i=1, 2, . . . l) of layers; and
σn2 denotes noise power, and Il, denotes an l-dimension unit matrix;
step 103: choosing the RI and PMI to which the maximum value in the metric values calculated in step 102 corresponds, as the information fed back to the transmission side.
Furthermore, the metric values may also be capacities, and the capacities to which all the RIs and PMIs in each layer correspond may be expressed as:
                              C                      n            ,            i                                (            l            )                          =                  log          (                      1                                                            σ                  n                  2                                ⁡                                  [                                                            (                                                                                                                                  (                                                                                                H                                  _                                                                n                                                                  (                                  l                                  )                                                                                            )                                                        H                                                    ⁢                                                                                    H                              _                                                        n                                                          (                              l                              )                                                                                                      +                                                                              σ                            n                            2                                                    ⁢                                                      I                            l                                                                                              )                                                              -                      1                                                        ]                                                            (                                  i                  ,                  i                                )                                              )                                    (        4        )            
where, Cn,i(l) denotes a capacity in the ith layer with a rank of l and a codebook index of n.
In the implementation of the present invention, the inventors found that at least the following defects existed in the prior art:
in step 101, the calculation of an effective channel matrix is an operation of matrix products with a relatively high complexity;
in step 102, in the calculation of metric values, it is necessary to calculate the inversion of positive definite Hermitian matrixes to which each codebook index and RI correspond in prior art, which requires multiple times of matrix inversion calculation with a very high complexity, thereby leading to relatively high consumption of power of the equipment;
for example, for a 4×4 MIMO system, the range of values of RI is 1-4, and the range of values of PMI is 0-15, hence, there are 64 combinations of RI and PMI. In the calculation of a MIMO effective channel, it is necessary to calculate a product of 4×4 matrixes and 4×1 vectors, a product of 4×4 matrixes and 4×2 matrixes, a product of 4×4 matrixes and 4×3 matrixes, a product of 4×4 matrixes and 4×4 matrixes for 16 times, respectively; in addition, it is necessary to perform an inversion operation to a Hermitian matrix composed of MIMO effective channel matrixes (the dimension of the Hermitian matrix is equal to RI), hence, matrix inversion operation is needed to be performed for totally 64 times (the case where RI=1 is considered as performing an inversion operation to matrixes with a dimension of 1), which leads to a high complexity of calculation.